Orientation - Siemens SINUMERIK 840D sl Function Manual

19.3.2

Orientation

The options for programming the orientation have been extended for 3D face milling.
The tool offset for face milling cannot be calculated simply by specifying the path (e.g. a line in
space). The surface to be machined must also be known. The control is supplied with the
information it requires about this surface by the surface normal vector.
The surface normal vector at the block beginning is programmed with A4, B4, C4, and the
vector at the block end with A5, B5, C5. Components of the surface normal vector that are
not programmed are set to zero. The length of a vector programmed in this way is irrelevant.
A vector of zero length (all three components are zero) is ignored, i.e. the direction
programmed beforehand remains valid, no alarm is generated.
If only the start vector is programmed (A4, B4, C4) in a block, then the programmed surface
normal vector remains constant over the entire block. If only the end vector is programmed
(A5, B5, C5), then large-circle interpolation is used to interpolate between the end value of
the preceding block and the programmed end value. If both the start and end vectors are
programmed, then interpolation takes place between both directions using the large-circle
interpolation method. The fact that the start vector may be reprogrammed in a block means
that the direction of the surface normal vector can change irregularly on a block transition.
Irregular transitions of the surface normal vector always occur in cases where there is no
tangential transition between the surfaces (planes) involved, i.e. if they form an edge.
Once a surface normal vector has been programmed, it remains valid until another vector is
programmed. In the basic setting, the surface normal vector is set to the same values as the
vector in the z direction. This basic setting direction is independent of the active plane (G17 -
G19). If ORIWKS is active, surface normal vectors refer to the active frame, i.e. when the
frame is rotated, the vectors rotate simultaneously. This applies both to programmed
orientations as well as to those derived from the active plane. If ORIWKS is active, the
surface normal vectors are adjusted when a new frame becomes active. An orientation
modified as the result of frame rotations is not returned to its original state on switchover from
ORIWKS to ORIMKS.
It must be noted that the programmed surface normal vectors may not necessarily be the
same as those used internally. This always applies when the programmed surface normal
vector is not perpendicular to the path tangent. A new surface normal vector is then
generated which is positioned in the plane extending from the path tangent to the
programmed surface normal vector, but which is at right angles to the path tangent vector.
This orthogonalization is necessary because the path tangent vector and surface normal
vector for a real surface must always be perpendicular to one another. However, since the
two values can be programmed independently, they may contain mutually contradictory
information. Orthogonalization ensures that the information contained in the path tangent
vector has priority over the data in the surface normal vector. An alarm is output if the angle
between the path tangent vector and the programmed surface normal vector is smaller than
the limit value programmed in machine data:
MD21084 $MC_CUTCOM_PLANE_PATH_LIMIT (minimum angle between surface normal
vector and path tangent vector)
If a block is shortened (inside corner), then the interpolation range of the surface normal
vector is reduced accordingly, i.e. the end value of the surface normal vector is not reached
as it would be with other interpolation quantities such as, for example, the position of an
additional synchronized axis.
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
W5: 3D tool radius compensation
19.3 Face milling
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